Viruses classified as HIV contain RNA as their genetic information and the infectivity of HIV depends upon the virus's ability to insert its genetic information into the DNA of a host. In order to insert its genetic information and therefore successfully infect a host, an HIV virus must convert its genetic material (RNA) into DNA so that the HIV genetic information is compatible with that of the host. Apparently, HIV is successful at converting its RNA into DNA, given the prevalence of AIDS. However, while the virus may successfully convert RNA into DNA, the conversion is seldom accurate. In other words, the DNA copy of the viral RNA is not always exact and the DNA copy can diverge from the viral RNA by several base pairs. Hence, while a host initially may be infected with a single virus particle, after several rounds of replication, the host may be infected with a genetically diverse population of viruses.
Although HIV is not uniformly classified, it is generally accepted that HIV 1 and HIV 2 are different viruses. Within each of these viral classifications are several groups or subtypes. For example, within the classification HIV 1, there is "group M", which is further classified into subtypes A-F, and "group O". HIV 2, on the other hand, contains subtypes A-E. Subtypes of HIV 1 and HIV 2 are broken down even further into categories to numerous to mention in this context. However, it is worth mentioning that all of these divisions are based upon the genetic variance between the viruses and, according to taxonomic theory, many of these viruses are the progeny of a single virus. Hence, the numerous HIV types and subtypes demonstrate the highly mutable nature of HIV and the genetic variability of the HIV genome.
The genetic variability of the virus can be attributed to the inefficiency with which the virus converts its RNA into DNA, as mentioned above. Another theory concerning the genetic variability of the virus is that hosts can be infected with multiple different populations of HIV (which as mentioned above, can arise out of an infection by a single virus) and through the course of replication and packaging of the viral genetic information, pieces of one viral genome can be recombined with pieces of another viral genome. Hence, upon packaging of the recombined genome, a genetically distinct virus is formed. Regardless of the manner by which the virus mutates, it is clear that viruses known as HIV have genomes that are highly mutable and are therefore constantly changing. This presents those searching for methods of detecting the virus based upon its genetic information with a constantly moving target.
Although it is known that certain regions of the HIV genome are conserved, this is not to say that these regions are immune from mutation particularly if mutations in these regions do not effect the structure of a protein encoded by these regions. Hence, developing reagents and methods for detecting HIV based upon its genetic information is a continuing challenge.